The present invention concerns improved hydraulic fluids and lubricating compositions. More particularly, there are provided novel combinations of additives for imparting improved properties to hydraulic fluids and gear lubricating compositions.
Hydraulic fluids are designed to transmit force and motion in a variety of industrial machines. They are used in hydraulic systems where the fluid is under pressure and in contact with moving parts. Often these moving parts have fine tolerances, a variety of metallurgy and operate at high volume, efficiency and pressure. Particularly desired characteristics of hydraulic fluids are good resistance to oxidation, wear, rust and corrosion. Deterioration of a hydraulic fluid caused by inadequate oxidation inhibition will adversely affect the hydraulic oil and its ability to transmit power efficiently and to lubricate the hydraulic system.
Filterability of a hydraulic oil can also be adversely affected if an oil is contaminated with water. Poor filterability of a hydraulic oil in contact with water will prevent the hydraulic system from transmitting force to the hydraulic motors.
The hydraulic oil must also have the ability to separate from water. Although small amounts of water can be tolerated, large amounts of water can attribute to rust, oxidation, decreased ability to lubricate and erratic pump action.
Because of the multifunctional nature of hydraulic oils, a commercially acceptable hydraulic fluid composition must meet established industry standards for all critical characteristics.
Particularly useful are antiwear hydraulic oils which possess wear characteristics and many of the performance characteristics of lubricating oils. In the past, antiwear hydraulic oils were formulated with zinc compounds, such as dithiophosphates and the like.
In addition to zinc compounds, antiwear hydraulic oils contain a complement of other additives necessary to prevent wear and deterioration of the equipment while the oil transmits the required power and motion. Lubricating compositions using zinc based antiwear additives contain other functional additives necessary to perform the lubricating function for a particular use. Thus, prior art teaches two different zinc based compositions specifically designed either for application as hydraulic fluids or for application as lubricants.
U.S. Pat. No. 4,383,931 teaches lubricating compositions containing the combination of sulfurized oil and methylenebis(dihydrocarbyldithiocarbamate) in conjunction with zinc dihydrocarbyldithiophosphate.
U.S. Pat. No. 3,876,550 discloses similar multifunctional combinations based on methylenebis(dihydrocarbyldithiocarbamate) in conjunction with a rust inhibitor of the succinic acid type. U.S. Pat. No. 3,359,203 teaches the use of adducts of dihydrocarbyldithiophosphoric acid and aliphatic esters of maleic or fumaric acid in conjunction with phenol type antioxidants.
U.S. Pat. No. 4,880,551 discloses a lubricating composition containing an antioxidant synergist consisting of 1-[di(4-octylphenyl)aminomethyl] tolutriazole, methylenebis(di-n-butyldithiocarbamate), and a phenolic antioxidant
U.S. Pat. No. 4,130,494 teaches that the load carrying capacity of synthetic lubricants is improved by adding a combination of organoamine salt of phosphate ester and organosulfonic acid ammonium salt.
U.S. Pat. No. 4,225,450 discloses lubricants that are stabilized with hydroxy-benzyl dithiocarbamates in conjunction with other lubricating antioxidants such as aromatic amines, sterically hindered phenols, esters of thiodipropionic acid, salts of dithiophosphoric acid, corrosion inhibitors such as benzotriazole, organic amines, amine salts of phosphoric acid partial esters, dinonylnaphthalenesulfonate salts and others.
None of the above referenced lubricating compositions possess the hydraulic function.
U.S. Pat. No. 3,658,706 discloses antioxidants for lubricating and functional fluids consisting of phosphorothionates and dihydrocarbylthioalkanoates.
Hydraulic oils contain metal corrosion inhibitors and rust inhibitors. U.S. Pat. No. 2,971,912 discloses benzotriazole type metal corrosion inhibitors. It is known to add sulfonate type rust inhibitors to zinc containing hydraulic oils as disclosed in U.S. Pat. No. 3,843,542, U.S. Pat. No. 3,923,669 and U.S. Pat. No. 3,791,976.
Environmental concerns linked to the toxicity of the heavy metal zinc has rendered zinc containing hydraulic oils undesirable. Disadvantageously, currently available antiwear hydraulic oils containing no or very low amounts of zinc have limited commercial use. These so called ashless antiwear hydraulic oils cannot satisfy all test standards; that is, they do not possess the varied and balanced properties required of antiwear hydraulic oils.
Surprisingly, it has been discovered that a synergistic combination of certain phosphates and sulfonates together with other functional additives impart to hydraulic oils the necessary balanced standard properties which allow the oil to perform the desired hydraulic functions even in the absence of zinc.